U.S. Pat. No. 7,132,581 concerns processes for converting oxygenates to olefins that include a step of pretreating catalyst used in the conversion reaction. A fresh or regenerated metalloaluminophosphate molecular sieve, which is low in carbon content, is pretreated with an aldehyde. The aldehyde forms a hydrocarbon co-catalyst within the pore structure of the molecular sieve, and the pretreated molecular sieve containing the co-catalyst is used to convert oxygenate to an olefin product.
U.S. Pat. No. 7,057,083 relates to processes for converting oxygenates to olefins that include a step of pretreating molecular sieve used in the conversion reaction with a C4-C7 olefin composition, which contains one or more C4-C7 olefins. Fresh or regenerated molecular sieve, which is low in carbon content, is contacted or pretreated with the olefin composition to form a hydrocarbon co-catalyst within the pore structure of the molecular sieve, and the pretreated molecular sieve containing the co-catalyst is used to convert oxygenate to a lighter olefin product.
U.S. Pat. No. 6,844,476 describes a method for converting heavy olefins present in a product stream exiting a first reaction zone into light olefins and carbonaceous deposits on a catalyst without separation of the heavy olefins from the product stream exiting the first reaction zone. The method comprises creating the product stream exiting the first reaction zone, the product stream exiting the first reaction zone comprising the heavy olefins, moving the product stream exiting the first reaction zone to a second reaction zone without separation of the heavy olefins from the product stream exiting the first reaction zone, and contacting the product stream exiting the first reaction zone with the catalyst under conditions effective to form the light olefins, the contacting causing the carbonaceous deposits to form on at least a portion of the catalyst.
US20060161035 describes the average propylene cycle yield of an oxygenate to propylene (OTP) process using a dual-function oxygenate conversion catalyst is substantially enhanced by the use of a combination of:
1) moving bed reactor technology in the catalytic OTP reaction step in lieu of the fixed bed technology of the prior art;
2) a separate heavy olefin interconversion step using moving bed technology and operating at an inlet temperature at least 15° C. higher than the maximum temperature utilized in the OTP reaction step;
3) C2 olefin recycle to the OTP reaction step; and
4) a catalyst on-stream cycle time of 700 hours or less. These provisions hold the build-up of coke deposits on the catalyst to a level which does not substantially degrade dual-function catalyst activity, oxygenate conversion and propylene selectivity, thereby enabling maintenance of average propylene cycle yield for each cycle near or at essentially start-of-cycle levels.
U.S. Pat. No. 5,914,433 relates to a process for the production of light olefins comprising olefins having from 2 to 4 carbon atoms per molecule from an oxygenate feedstock. The process comprises passing the oxygenate feedstock to an oxygenate conversion zone containing a metal aluminophosphate catalyst to produce a light olefin stream. A propylene stream and/or mixed butylene is fractionated from said light olefin stream and butylenes and heavies cracked to enhance the yield of ethylene and propylene products. This combination of light olefin product and butylene and heavies cracking in a riser cracking zone or a separate cracking zone provides flexibility to the process which overcomes the equilibrium limitations of the aluminophosphate catalyst. In addition, the invention provides the advantage of extended catalyst life and greater catalyst stability in the oxygenate conversion zone. In said process the effluent of the riser cracking zone or the separate cracking zone is sent to the oxygenate conversion zone.
It has now been discovered a more efficient process to make light olefins, in particular propylene and aromatics from oxygenates. This invention relates to a process including three zones: a XTO reaction zone containing catalyst wherein “X” (e.g. oxygenates) are converted into mainly light olefins, an OC reaction zone containing substantially the same catalyst wherein heavier olefins and optionally ethylene are converted into aromatics and additional light olefins and a zone wherein the catalyst used in the other two zones is regenerated (the catalyst regeneration zone also referred as the regeneration zone). This invention relates to processes for converting oxygenates to olefins over a zeolite-based catalyst (in the XTO reaction zone) that include a step of primarily using the zeolite-based catalyst in the conversion reaction (the OC reaction zone) with a substantially olefinic feedstock, which contains one or more C2-C12 olefins, and forming by way of example 0.1 wt % or more of coke-like deposition on the molecular sieves. The main role of this hydrocarbons deposition is in selective deactivation of the non-selective acid sites. This contact of the molecular sieve with an olefinic feedstock could be performed in the presence or in absence of water and oxygenated compounds. In a most preferred embodiment, this contact is performed in the absence of water and oxygenated compounds. It was found that the primarily use (as a pre-treatment) of zeolite-based catalyst for the conversion of olefinic feedstock in the OC reaction zone provides a catalyst with significantly improved catalyst performance for the MTO reaction in the XTO reaction zone. Without willing to be bound to any theory, it is believed that the effect consists in a selective poisoning of the non-selective acid sites at the external surface which are responsible typically for side-reaction, resulting in enhanced formation of paraffins. In the present invention we are talking about selectively pre-deactivated catalyst in which the deposited coke has no catalytic activity as is in the case of coke co-catalyst on SAPO-type materials.
Another advantage in using the olefin compositions of this invention for the primarily use of zeolite-based catalyst is that this provides a way to reduce undesirable by-products in the overall conversion of oxygenates to olefins. Typically, heavier olefins such as the C4-C7 olefins are considered as undesirable by-products, because the value of those olefins are considerably lower than ethylene and propylene. Therefore, the by-products of the oxygenate to olefins reaction process can be used to enhance selectivity of the catalyst to provide aromatics and the more desirable ethylene and propylene products.
Advantages of the present invention:                Perform the reaction in each operating zone under optimal conditions        Optimal catalyst selectivity by primarily use of the catalyst for olefin cracking        Better heat integration between the different reactor zones        
It is preferred that the catalyst in the three zones is in the fluidised state. This allows easy transport of catalyst from one zone to other zones.
The conversion of X is carried out in a separate zone than the conversion of ethylene or C4-C7 hydrocarbons. This allows optimising each reaction conditions separately. The conversion of X is a strongly exothermic conversion and is hence best performed in a fluidised bed with substantially homogenous temperature throughout the catalyst bed, wherein the temperature is regulated by injecting the feed at a temperature lower than the reaction temperature (cold feed serves as heat sink) or by cooling the catalyst by means of a catalyst cooler by raising steam in a heat exchanger. The conversion of C4-C7 olefins is on the contrary an endothermic or slightly exothermic reaction. The heat of reaction can be provided by super-heating the feedstock so that the outlet temperature of the reactor is sufficiently high to obtain a sufficiently high conversion of the feedstock. The heat of reaction can also be provided by means of a high catalyst circulation rate at sufficiently high temperature to convert the feedstock. This can easily be done in a fluidised bed reactor with catalyst injection at the bottom of the reactor (inlet) with catalyst separation at the top of the reactor (outlet). Sufficiently hot catalyst can come from the regenerator where by combustion of coke deposited on the catalyst with air in a controlled manner. In order to maximise combustion rate and minimise the combustion temperature, combustion promoters are added, known by the persons in the art. The combustion promoters consist of platinum on alumina carriers. In case not enough coke is deposited during conversion of X or of C4-C7 olefins, additional fuel can be injected in the regenerator to provide heat to heat up more catalyst so that more heat can flow to the C4-C7 conversion zone. Examples of additional fuel are natural gas, LPG, heating oil or synthesis gas. In particular CO-rich synthesis gas is suitable. This CO-enriched synthesis gas is readily available in a methanol synthesis plant as for instance the purge stream of the methanol synthesis reactor loop.
Another source of hot catalyst is the XTO reactor zone as the conversion of X is strongly exothermic. The temperature of the catalyst, leaving the XTO zone should be at least higher than the temperature required at the outlet of the C4-C7 olefin conversion zone in order to obtain sufficient conversion. The conversion of C4-C7 olefins on hot catalyst conveying from the XTO zone is a kind of catalyst cooler for the XTO reaction zone.
Although, it is better to perform the conversion of X-containing compound and of the C4-C7 olefins in separate reaction zones like described above in the XTO and OC reaction zone respectively, the olefins cracking being endothermic can be done by combining at least a part of the X-containing compound with the C4-C7 olefins in the OC reaction zone. The amount of X-containing compound converted should reduce the temperature loss due to the endothermic C4-C7 olefins cracking. The amount should advantageously not exceed the value when the combined conversion becomes exothermic.